I lived in Mexico City for 12 years, and these are the best tacos I found in the city of great…read moretacos! The "business" is a tarp covering with portable preparation equipment that is set-up every night, except Tuesdays. Tacos are ready for consumption at about 8:00 p.m. and the business remains open until the food is gone, usually in the early morning - 3:00 a.m. to 4:00 a.m. These are street tacos, with no place to sit and very limited parking and you need to make sure the servers know you are there. The tacos are well worth the trip to the far west side of the city. If you take a cab to get there, consider buying dinner for your cabbie, so you have a return ride.
Tacos al pastor (those on the vertical rotisserie) are excellent, as are the bistek (steak), chuleta (pork chop). Try them all! I prefer them with just a touch of salsa, so as not to hide the taste of the meat.